**3.6 Seeding process**

For the seeding process, 100 ml of GNPs and 10 ml of functionalized silica were magnetically stirred in a 140 ml glass flask for 5 min as shown in **Figure 3a**. Then, it was left still for 2 h. **Figure 3b** presents how the seeded silica spheres precipitated and changed their color from opaque white to lavender, while the mother solution changed from wine red to transparent. The mixture was centrifuged at 6000 rpm for 2 min and washed in deionized water three times. Finally, it was sonicated in 20 ml of deionized water final volume. The same procedure was followed, but the solution was left still for only 30 min to observe the development of the seeding process through time.
